Structural characterization of oligosaccharides from free radical depolymerized fucosylated glycosaminoglycan and suggested mechanism of depolymerization

Free radical depolymerization is a common method in structural analysis of polysaccharides, the major challenge is the analysis of the cleavage site and characterization of newly formed ends in this reaction. Here, a fucosylated glycosaminoglycan from H. fuscopunctata (HfFG) was depolymerized by H2O2 and a series of oligosaccharides were purified and their structures were elucidated. For non-reducing ends of the trisaccharides were intact GalNAc4S6S, the cleavage site should mainly be the β(1,3) linkages between GlcA and GalNAc in the backbone of FG. Meanwhile, the reducing ends of the disaccharides and trisaccharides were almost dicarboxylic acid derivatives of GlcA, possibly arising from oxidative breaking of the CC bond of GlcA at the reducing ends. In addition, glycosidic linkages in D-GalNAc-β(1,4)-D-GlcA and L-FucS-α(1,3)-D-GlcA located at the reducing end could be cleaved, and the released GalNAc4S6S were oxidized to N-acetylgalactosaminic acid.